Method and system of dry processing of converter slag in copper smelting

ABSTRACT

A method for processing converter slag produced in copper smelting includes feeding the converter slag into a reducing furnace, reducing zinc and copper contained in the converter slag by heating and removing the reduced zinc through volatilization in a reducing furnace. The slag discharged from the converter is transformed into a raw material for iron making.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and a system of dry processing of slag discharged from a converter in copper smelting, and in particular, to a method and a system of dry processing of slag discharged from a converter in copper smelting, for transforming the slag into a raw material for iron making.

2. Description of the Related Art

A general process of copper smelting is outlined below. Raw material copper concentrate is oxidized in a flash furnace to form matte having a copper content of about 68% and flash furnace slag composed largely of iron oxide and silicic acid. The matte and the slag are separated. The matte is fed into a converter to form blister copper having a copper content of about 99% and converter slag composed primarily of iron oxide silicates. The copper and the slag are separated. The blister copper is cast into an anode having a higher copper purity. The anode is electrolytically-refined to make electrolytic copper.

On the other hand, slag beneficiation is primarily applied to the converter slag, which is solidified and crushed for a floatation process to recover copper (Journal of the Mining and Materials Processing Institute of Japan, 1993. 12, Vol. 109, Feature Issue on Nonferrous Smelting, pp. 964-970 (hereinafter referred to as Nonpatent Document 1) and Journal of the Mining and Materials Processing Institute of Japan, 1997. 12, Vol. 113, Feature Issue on Recycling, p. 996, the last paragraph on the left column (hereinafter referred to as Nonpatent Document 2)). In the slag beneficiation process, copper concentrate having a high copper content (about 25% Cu) and iron concentrate having a low copper content (about 0.6% Cu) are separated. The slag copper concentrate can be reprocessed in a flash furnace, while the iron concentrate can be recycled as a raw material primarily for cement.

Furthermore, Japanese Unexamined Patent Application Publication No. 53-22115 discloses a method for processing slag to reduce copper oxide and Fe₃O₄ contained in molten converter slag by blowing a solid reductant, such as coke and coal, a gas reductant, or a liquid reductant into the slag to produce copper-removed slag having a copper content of not more than 1% Cu and blister copper.

The Caletones refinery of Codelco in Chile uses a practical method for recovering copper in slag by blowing pulverized coal into molten converter slag to reduce magnetite in the slag (Rolando Campos and Luis Torres, CALETONES SMELTER: TWO DECADES OF TECHNOLOGICAL IMPROVEMENTS, The Paul E. Queneau International symposium, Ontario, CANADA (1993) (hereinafter referred to as Nonpatent Document 3).

A new route for recycling converter slag is required, since the recent shrinking trend in the cement industry in Japan has created difficulty in finding firms receiving the iron concentrate produced through a slag beneficiation process, as described in Nonpatent Document 1. Since the converter slag contains about 50% by mass of iron, there is a possibility for the use as a raw material for iron-making. However, since the converter slag contains about 4% by mass of copper and about 2% by mass of zinc, the contents of copper and zinc are too high to use the slag as a raw material for iron making. Also iron concentrate produced through a slag beneficiation process contains about 0.6% by mass of copper and about 2.5% by mass of zinc, which may be too high to use the concentrate as a raw material for iron making. The contents of not more than 0.3% by mass of copper and not more than 1% by mass of zinc may be desired for the use as a raw material for iron making. However, since converter slag processed by a method described in Nonpatent Document 2 or 3 also has high copper and zinc contents for use as a raw material for iron making, it may not be recommended for the use as a raw material for iron making.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and system of processing of slag discharged from a converter in copper smelting for transforming the slag into a raw material for iron making.

Through extensive research for solving the problem, the present inventors have discovered a method for processing slag to remove zinc through volatilization from the slag and to reduce copper oxide in a reducing furnace by a slag-fuming process used widely in zinc smelting and, subsequently, to separate the reduced blister copper from the slag by sedimentation in the reducing furnace or in a settling furnace arranged in series with the reducing furnace after the slag is transferred thereto. According to the present method, the copper and zinc contents in the converter slag can be reduced to levels suitable for use as a raw material for iron making. Also, the converter slag can be continuously processed through the sedimentation separation in the settling furnace as a separate process, not in the reducing furnace.

In a general slag-fuming process, molten slag is chemically reduced by heating, and then metals such as Zn, Pb and As are volatilized, for example, in a reducing furnace having a gas-blowing lance or a tuyere located in the lower portion of the furnace. This process involves reduction and volatilization of metals in the slag by squirting a reductant (e.g. propane or heavy oil) and combustion air into the slag charged in the furnace. The processed slag is drained from the bottom of the furnace and the volatized metals are recovered from the top of the furnace.

Although a slag-fuming process is commonly used in processing slag in zinc smelting, it has not been conventionally applied to processing of converter slag in copper smelting explained in the present invention and not been required either. The feature of the present invention is, therefore, that a slag-fuming process is applied to processing of converter slag in copper smelting. Alternatively, in an embodiment, drained slag from a reducing furnace is transferred to a settling furnace and the reduced copper is separated by sedimentation and recovered there. In this case, continuous processing of converter slag is possible, which is very favorable to actual operation.

Accordingly, an aspect of the present invention provides a method for processing converter slag produced in copper smelting, encompassing feeding converter slag into a reducing furnace, reducing zinc and copper contained in the converter slag by heating and removing the reduced zinc through volatilization in the reducing furnace.

Another aspect of the present invention provides a method for processing converter slag produced in copper smelting, encompassing feeding converter slag into a reducing furnace, reducing zinc and copper contained in the converter slag by heating, removing the reduced zinc through volatilization, and separating the reduced copper from the slag by sedimentation in the reducing furnace.

A further aspect of the present invention provides a method for processing converter slag produced in copper smelting, encompassing feeding converter slag into a reducing furnace, reducing zinc and copper contained in the slag by heating, removing the reduced zinc through volatilization in the reducing furnace, subsequently transferring the reduced copper and the slag to a settling furnace from the reducing furnace, and separating the reduced copper from the slag by sedimentation in the settling furnace.

In an embodiment of the present invention, the method further encompasses crushing the slag after sedimentation separation of the reduced copper from the slag.

In another embodiment of the present invention, the method further encompasses reducing Fe₃O₄ contained in the slag to FeO by heating in the reducing furnace.

In a further embodiment of the present invention, the method further encompassing feeding the converter slag from a holding furnace into the reducing furnace, wherein the holding furnace retains the converter slag in a molten state and controls the feed rate of the converter slag to the reducing furnace.

A further aspect of the present invention provides a system for processing converter slag produced during copper smelting encompassing a reducing furnace that reduces zinc and copper contained in the converter slag by heating, discharging means configured to remove the volatile reduced zinc, the discharging means being provided in the reducing furnace, and draining means configured to drain the reduced copper separated by sedimentation from the reducing furnace.

In an embodiment of the present invention, the system further encompasses crushing means configured to crush the slag and transferring means configured to transfer the slag discharged from the reducing furnace to the crushing means.

Another aspect of the present invention provides a system for processing converter slag produced during copper smelting encompassing a reducing furnace configured to reduce zinc and copper contained in the converter slag by heating, discharging means configured to remove the volatile reduced zinc, the discharging means being provided in the reducing furnace, a settling furnace configured to separate the reduced copper by sedimentation, transfer means configured to transfer the slag discharged from the reducing furnace to the settling furnace, and draining means configured to drain the reduced copper separated by sedimentation from the settling furnace.

In an embodiment of the present invention, the system further includes crushing means configured to crush the slag and transferring means configured to transfer the slag discharged from the reducing furnace to the settling furnace.

In another embodiment of the present invention, the system further includes a holding furnace configured to maintain the converter slag in a molten state and configured to control a feed rate of the converter slag to the reducing furnace and transfer means configured to transfer the converter slag discharged from the holding furnace to the reducing furnace.

According to the present invention, converter slag can be continuously transformed to slag containing copper and zinc in reduced amounts suitable for use as a raw material for iron making.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary diagram of a system for continuous processing of converter slag of the invention.

FIG. 2 shows an exemplary diagram of a system for batch processing of converter slag of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENT OF THE INVENTION

A method and a system of processing of converter slag according to an embodiment of the present invention are explained below with reference to FIGS. 1 and 2.

In general, slag discharged from a converter in copper smelting has a composition that contains 50 to 60% by mass of iron (primarily composed of Fe₃O₄ and FeO), 20 to 25% by mass of silicon (primarily composed of SiO₂), 3 to 5% by mass of copper (primarily composed of CuS, Cu₂O and CuO), 3 to 6% by mass of zinc (primarily composed of ZnO), 1 to 3% by mass of aluminum (primarily composed of Al₂O₃).

Accordingly, the term “converter slag” used in the present invention refers to not only slag actually discharged from a converter in copper smelting but also slag having a similar composition to that of the converter slag in copper smelting. For example, slag in a flash furnace contains about 3 to 5% of Al₂O₃ derived from a raw material ore and flux silicates ore. The content of alumina (Al₂O₃) is too high to use the slag as a raw material for iron making. However, when the contents of alumina in a raw material ore and a silicates ore are low and when the content of alumina in flash furnace is low, the present invention can be applied.

—System for Continuous Processing—

A system for continuous processing of converter slag is now described. With reference to FIG. 1, slag flowing into a receiving trough 1 from a converter (not shown) in a molten state at 1250 to 1330° C. is introduced into a holding furnace 2 while maintaining the molten state. Alternatively, the slag may be introduced to the holding furnace 2 not in the molten state. For example, granular slag received in a hopper may be introduced to the holding furnace 2. The slag introduced to the holding furnace 2 is retained in the molten state. The holding furnace 2 can control the feed rate of the slag to a reducing furnace 4. For example, feeding the slag into the reducing furnace 4 at a constant flow rate contributes to stabilization of the continuous operation of the system for processing the slag.

The slag coming out of the holding furnace 2 passes through a slag trough 3 and is fed into the reducing furnace 4. In the reducing furnace 4, zinc, copper and other metal constituents are reduced. A substantial amount of magnetite (Fe₃O₄), which is contained in the slag, is reduced to FeO, resulting in a reduction in the viscosity of the slag. Since the lower viscosity of the slag enhances sedimentation separation of the reduced copper suspended in the slag, a higher recovery rate of copper in the subsequent step is achieved.

Nonlimiting examples of reductants include solid carbonaceous reductants such as coke and coal, gaseous reductants such as hydrogen and hydrocarbons (e.g. methane, ethane, propane, and butane), and liquid reductants such as petroleum and heavy oil. Typically, liquefied petroleum gas (LPG) can be used. In a preferred embodiment, the reductant and combustion air are squirted into the slag in the furnace 4 by top blowing from the head of a lance 5 extending from the top of the reducing furnace 4. Such blowing leads to intense agitation of the molten slag in the reducing furnace 4, resulting in enhanced reaction efficiency of the slag and the reductant. The head of the lance 5 may be immersed in the slag. Alternatively, the reductant may be supplied using a tuyere located at the bottom of the furnace. Increasing the flow rate of the reductant to be introduced or the reduction time enhances the efficiency of the reduction reaction. In other words, the contents of zinc and copper in the slag can be reduced.

In the reducing furnace 4, for example, when propane is used as a reductant, the following reduction reactions occur.

10Cu₂O+C₃H₈→20Cu+3CO₂+4H₂O

10ZnO+C₃H₈→10Zn+3CO₂+4H₂O

10Fe₃O₄+C₃H₈→30FeO+3CO₂+4H₂O

The reduced zinc is volatilized from the slag phase and is discharged from a chimney 6 as a slag-fuming material together with other volatile components or fine slag particles. A bag filter 7 is installed in the flue to recover the zinc. In addition, cooling water may be sprayed to the flue or a water-cooling tower (not shown) may be installed, for the purpose of decreasing the temperature of the exhaust gas. Alternatively, the reduced zinc may be recovered as zinc oxide through oxidization by the air on the way to the chimney 6. In general, lead is also contained in the slag-fuming dust.

After the reduction reactions, the slag containing reduced copper is discharged from the reducing furnace 4, passes through melt trough 8, and is introduced to a settling furnace 9 in the molten state. The reduced copper is separated thereat by sedimentation caused by a difference in specific gravity. Continuous operation can be achieved by sedimentation separation in the settling furnace 9, not in the reducing furnace 4. Increasing the time for the sedimentation separation enhances the efficiency of the sedimentation separation and reduces the content of copper in the slag. Conversely, the efficiency of copper recovery can be improved.

After the sedimentation separation, the reduced copper is drained from a blister copper trough 10. The reduced copper may contain 60 to 80% by mass of copper and be recycled into a converter. On the other hand, the slag separated from the reduced copper passes through a slag trough 11 and is transferred to a slag-crushing unit 12 to be crushed into grains having sizes suitable for use. Nonlimiting examples of the crushing unit include a water-granulation machine, a crusher, a mill, and a combination thereof.

Through the processes described above, the content of copper in the slag can be reduced to 0.3% by mass or less and the content of zinc to 1% by mass or less. The slag processed according to the present invention can, therefore, be used as a raw material for iron making.

According to an embodiment of the present invention, converter slag can be continuously processed. Consequently, a continuous run of the system enables the reduction reactions and removal of the reduced zinc by volatilization in the furnace, the sedimentation separation of the reduced copper in the settling furnace, and the crushing of the slag in the crushing unit to concurrently proceed.

—System for Batch Processing—

Next, a system for batch processing of converter slag is described. With reference to FIG. 2, slag flowing into a receiving trough 1 from a converter (not shown) in a molten state at 1250 to 1330° C. is introduced into a reducing furnace 4 while maintaining the molten state. In the reducing furnace 4, zinc, copper, and other metal components are reduced. The reductant suitable for use and the reduction reactions in the reducing furnace 4 are similar to those in the system for continuous processing. Also, the reduced zinc is recovered as in the system for continuous processing.

After the reduction reactions, the reduced copper is separated by sedimentation in the reducing furnace 4. After the sedimentation separation, the reduced copper is drained from a blister copper trough 10. On the other hand, the slag separated from the reduced copper passes through a slag trough 11 and is transferred to a slag-crushing unit 12 to be crushed into grains having sizes suitable for use. The processed slag can be used as a raw material for iron making. A plurality of reducing furnaces may be arranged in parallel.

EXAMPLES

Examples of the present invention are described below. The examples are merely illustrative, and not limiting the invention.

Test 1 (Crucible Test)

Slag (1.1 kg) discharged from a converter during copper smelting was put in a crucible in a nitrogen atmosphere and was melted at 1250° C. Subsequently, propane gas at a flow rate of 8.25 L/hr and air at a flow rate of 8.25 L/hr were bubbled into the crucible for one hour to reduce copper, zinc and magnetite (Fe₃O₄) in the slag. During the reduction reactions, reduced zinc as a product was removed through spontaneous volatilization from an opening of the crucible. Then, reduced copper as a product was separated by settling from the slag. Variations in the contents of copper and zinc in the slag before and after the test are shown in Table 1.

TABLE 1 Content of Cu (% by mass) Content of Zn (% by mass) Before reduction After settling Before reduction After settling 3.9% 0.2% 3% 1%

Test 2 (Simulated Actual Operation Test 1)

Table 2 shows calculated values of a continuous operation under predetermined conditions in the system shown in FIG. 1, in view of the crucible test described above. The simulated operational conditions are as follows.

Dimensions of reducing furnace: 3 m (diameter) by 8 m (height) (56 m³)

Temperature of molten metal: 1250° C.

Reduction time: 1 hr

Reductant: LPG (436 kg/hr)+Air (3,178 Nm³/hr)

Settling time: 1 hr

TABLE 2 Content of Cu Content of Zn Throughput (t/h) (% by mass) (% by mass) Converter slag 27 5.5 2.5 (raw material) Slag after separation 25 0.3 0.7 of reduced copper Reduced copper 2 74.2 0.1

Test 3 (Simulated Actual Operation Test 2)

According to the crucible test results as described above, when the system shown in FIG. 1 is in continuous operation under other predetermined conditions, the calculated results for the assumed processing are described in Table 3. The simulated operational conditions are as follows.

Dimensions of reducing furnace: 3 m (diameter) by 8 m (height) (56 m³)

Temperature of molten metal: 1250° C.

Reduction time: 1 hr

Reductant: Heavy oil (605 kg/hr)+Air (3,883 Nm³/hr)

Settling time: 1 hr

TABLE 3 Content of Cu Content of Zn Throughput (t/h) (% by mass) (% by mass) Converter slag 27 5.5 2.5 (raw material) Slag after separation 25 0.3 0.7 of reduced copper Reduced copper 2 74.2 0.1 

1. A method for processing converter slag produced in copper smelting, comprising: feeding converter slag into a reducing furnace; reducing zinc and copper contained in the converter slag by heating; and removing the reduced zinc through volatilization in the reducing furnace.
 2. The method according to claim 1, further comprising: separating the reduced copper from the converter slag by sedimentation in the reducing furnace.
 3. The method according to claim 1, further comprising: transferring the reduced copper and the converter slag to a settling furnace from the reducing furnace; and separating the reduced copper from the converter slag by sedimentation in the settling furnace.
 4. The method according to claim 2, further comprising: crushing slag after the sedimentation separation of the reduced copper from the converter slag.
 5. The method according to claim 3, further comprising: crushing slag after the sedimentation separation of the reduced copper from the converter slag.
 6. The method according to claim 1, further comprising: reducing Fe₃O₄ contained in the converter slag to FeO by heating in the reducing furnace.
 7. The method according to claim 2, further comprising: reducing Fe₃O₄ contained in the converter slag to FeO by heating in the reducing furnace.
 8. The method according to claim 3, further comprising: reducing Fe₃O₄ contained in the converter slag to FeO by heating in the reducing furnace.
 9. The method according to claim 1, wherein the converter slag is fed from a holding furnace into the reducing furnace, the holding furnace retains the converter slag in a molten state and controls a feed rate of the converter slag to the reducing furnace.
 10. The method according to claim 2, wherein the converter slag is fed from a holding furnace into the reducing furnace, the holding furnace retains the converter slag in a molten state and controls a feed rate of the converter slag to the reducing furnace.
 11. The method according to claim 3, wherein the converter slag is fed from a holding furnace into the reducing furnace, the holding furnace retains the converter slag in a molten state and controls a feed rate of the converter slag to the reducing furnace.
 12. The method according to claim 4, wherein the converter slag is fed from a holding furnace into the reducing furnace, the holding furnace retains the converter slag in a molten state and controls a feed rate of the converter slag to the reducing furnace.
 13. The method according to claim 5, wherein the converter slag is fed from a holding furnace into the reducing furnace, the holding furnace retains the converter slag in a molten state and controls a feed rate of the converter slag to the reducing furnace.
 14. A system for processing converter slag produced during copper smelting comprising: a reducing furnace configured to reduce zinc and copper contained in converter slag by heating; discharging means provided in the reducing furnace, configured to discharge the volatile reduced zinc; and draining means configured to drain the reduced copper separated by sedimentation from the reducing furnace.
 15. The system according to claim 14, further comprising: crushing means configured to crush the converter slag; and first transferring means configured to transfer the converter slag discharged from the reducing furnace to the crushing means.
 16. The system according to claim 15, further comprising: a holding furnace configured to maintain the converter slag in a molten state and configured to control a feed rate of the converter slag to the reducing furnace; second transfer means configured to transfer the converter slag discharged from the holding furnace to the reducing furnace.
 17. A system for processing converter slag produced during copper smelting comprising: a reducing furnace configured to reduce zinc and copper contained in converter slag by heating; discharging means provided in the reducing furnace, configured to discharge the volatile reduced zinc; a settling furnace configured to separate the reduced copper from the converter slag by sedimentation; first transfer means configured to transfer the converter slag discharged from the reducing furnace to the settling furnace; and draining means configured to drain the reduced copper separated by sedimentation from to the settling furnace.
 18. The system according to claim 17, further comprising: crushing means configured to crush the converter slag; and second transfer means configured to transfer the converter slag discharged from the settling furnace to the crushing means.
 19. The system according to claim 17, further comprising: a holding furnace configured to maintain the converter slag in a molten state and configured to control a feed rate of the converter slag to the reducing furnace; second transfer means configured to transfer the converter slag discharged from the holding furnace to the reducing furnace.
 20. The system according to claim 18, further comprising: a holding furnace configured to maintain the converter slag in a molten state and configured to control a feed rate of the converter slag to the reducing furnace; third transfer means configured to transfer the converter slag discharged from the holding furnace to the reducing furnace. 